1. Field of the Invention
The present invention relates to improved apparatus and novel methods of operation for cargo container handling cranes having a horizontal gantry supported at an elevated location above the cargo container pickup and deposition areas. More particularly, the present invention relates to the apparatus and method for reducing cargo container handling and transfer cycle times by employing positive residual sway arrest and automatic container transfer in a cargo container handling crane which transports containers horizontally along the gantry of the crane.
A computer controlled shuttle is utilized by the present invention whereby cargo containers can be simultaneously lifted and lowered independently at opposite ends of the crane gantry while concurrently containers are transported along the gantry by the shuttle. Residual sway in the container pickup apparatus during lowering is arrested by passing it through a guide chute near the end of the lowering cycle.
2. Description of the Prior Art
The handling and protection of cargo and material during its transportation has been greatly facilitated by the advent of containerization many years ago. Rail mounted dockside gantry cranes having retractable booms have now been long accepted as the standard in the industry for loading and unloading containerized cargo and fungible bulk materials. The containers are moved by the cranes between waterborne vessels and dockside transportation equipment.
When a cargo container transport ship is berthed alongside a dock, a gantry crane is moved along the dock parallel to the ship to a position where a retractable boom can be extended across the beam of the ship above the ship's cells which are the cargo container carrying area. The retractable boom in its operating position extends horizontally outboard from the crane's superstructure and, in its retracted position, clears the superstructure of any ship berthed alongside the dock adjacent to the crane. Containers can be transported along the gantry of the crane between the dockside pickup and deposition area and any storage position located within the beam of a berthed ship in its holds or on its deck.
In the particular form of a gantry crane to which the present invention pertains, the purpose is to move cargo containers a specific horizontal distance from a pickup area to a deposition area. In each operation, in the most usual situation, the pickup area is either a dockside location where a container is picked off of a flatbed trailer or transport truck or railroad car, and moved outboard by the crane and lowered into a shipboard cargo container cell, or the reverse, wherein a container is lifted from a cell onboard ship and moved to a dockside storage area or a truck, trailer or railroad car.
The gantry portion of the cargo container handling crane of the preferred embodiment of the present invention includes the retractable boom and a dockside portion and a rear extension of said boom supported by the crane superstructure. However, it is applicable to any crane wherein containers are moved along a gantry from a pickup position to a deposition area. Trolleys run along the gantry and suspend cargo container lifting spreaders from fleet-through wire rope reeving for attaching to and picking up cargo containers.
In a transfer cycle by a crane, the container must first be picked up, then lifted vertically, moved horizontally, and then lowered to its deposition area. During a portion of the move, vertical and horizontal movement of the container can occur simultaneously. However, for each transfer cycle, the crane must raise or lower a container a specific distance to clear the side of a ship, and a round trip transfer cycle takes a substantial period of time to handle one container.
In addition to the transfer cycle time required to pickup, lift, move, lower, and deposit the container, there is also a delay at each end of the cycle if sway or pendulum movement is induced into the load by virtue of the starting and stopping of the horizontal movement of the container along the gantry. It takes additional time to abate the sway and to position the container by selectively controlling the forward and reverse movement of the trolley.
A more recent development in the field of cargo container handling is the development of the hatch coverless container ships which unfortunately has increased the container transfer cycle time in the prior art gantry cranes. These ships were developed to reduce lashing work or container tie down time for containers stacked on the open deck of the ship. This development provides cell guides which project upwards from the deck of the ship and which therefore require every vertical movement of a container to clear not only the side of the ship but the tops of all the upward projecting cell guides as well which previously did not extend above the ship's deck.
Therefore, in comparison, when loading and unloading the old type of ship, the container did not always have to be fully lifted a specified height above the deck of the ship. It was only necessary to clear the deck of the ship until containers began to be stacked on top of the deck. At that point, it was still necessary only to lift containers over those already stacked on the deck although when a ship is properly loaded and unloaded, it is accomplished in a way in which the outboard containers are placed on the ship first and unloaded last so that subsequent containers do not have to be lifted over more than the minimum height of on-deck containers than is necessary.
Therefore, the container handling productivity for hatch coverless ships is considerably lower in comparison with conventional container ships because the handling pass or transfer cycle on the latter is substantially shorter until stacked containers on the ship gradually increase the time of the handling pass or transfer cycle.
One method of improving the speed of operation of a crane is to provide a twin lift crane in which two containers are handled at the same time by the crane. However, this requires nearly a complete duplication of machinery: at least twin booms and two-thirds the superstructure of two cranes, but the crane can handle two containers simultaneously by the same number of operators.
The present invention overcomes the limitations of the prior art by providing a single gantry crane which lowers the cycle transfer time by handling several containers simultaneously and by arresting residual sway of the cargo container lifting apparatus. It includes new and novel apparatus and methods of operation. A pair of trolleys on the gantry of the crane are dedicated to lifting and lowering the load and do not horizontally traverse with it. An automatic shuttle is provided which traverses the gantry between the two lifting and lowering trolleys and horizontally transports containers between the trolleys. This allows three containers to be handled almost simultaneously, one being lifted, one being transported horizontally, and one being lowered. In addition, the positioning of the lifting spreader for the purpose of picking up a container or for depositing it underneath the superstructure of the crane is aided by a container guide chute which arrests the residual sway in the lifting spreader at the shoreside end of the crane.